U.S. patent application number 12/406321 was filed with the patent office on 2009-10-01 for display particles for image display apparatus and image display apparatus.
This patent application is currently assigned to Konica Minolta Business Technologies, Inc.. Invention is credited to Yukio HOSOYA, Hiroyuki KONNO, Tatsuya NAGASE, Okushi OKUYAMA, Shigeki TAKENOUCHI, Satoshi UCHINO.
Application Number | 20090242847 12/406321 |
Document ID | / |
Family ID | 41115702 |
Filed Date | 2009-10-01 |
United States Patent
Application |
20090242847 |
Kind Code |
A1 |
HOSOYA; Yukio ; et
al. |
October 1, 2009 |
DISPLAY PARTICLES FOR IMAGE DISPLAY APPARATUS AND IMAGE DISPLAY
APPARATUS
Abstract
Display particles, which are used for an image display apparatus
having a structure in which the display particles in a powdered
state are sealed between two substrates at least one of which is
transparent, and by generating an electric field between the
substrates, the display particles are moved so that an image is
displayed, comprising: base particles A containing at least a resin
and a colorant, and having a volume-average particle size D1 of 1
to 50 .mu.m; resin fine particles B being externally added to the
base particles, and having an average primary particle size D2 of
30 to 250 nm; and inorganic fine particles C being externally added
to the base particles, and having an average primary particle size
D3 of 5 to 30 nm, wherein the display particles for an image
display apparatus are designed so that D1, D2 and D3 satisfy
10.ltoreq.D1/D2.ltoreq.1000 and 2.ltoreq.D2/D3.ltoreq.50, and an
image display apparatus provided with such particles for an image
display apparatus.
Inventors: |
HOSOYA; Yukio; (Tama-shi,
JP) ; OKUYAMA; Okushi; (Hachioji-shi, JP) ;
UCHINO; Satoshi; (Hino-shi, JP) ; KONNO;
Hiroyuki; (Hachioji-shi, JP) ; NAGASE; Tatsuya;
(Tachikawa-shi, JP) ; TAKENOUCHI; Shigeki;
(Chofu-shi, JP) |
Correspondence
Address: |
BUCHANAN, INGERSOLL & ROONEY PC
POST OFFICE BOX 1404
ALEXANDRIA
VA
22313-1404
US
|
Assignee: |
Konica Minolta Business
Technologies, Inc.
Chiyoda-ku
JP
|
Family ID: |
41115702 |
Appl. No.: |
12/406321 |
Filed: |
March 18, 2009 |
Current U.S.
Class: |
252/500 |
Current CPC
Class: |
G02F 2001/1678 20130101;
G02F 1/167 20130101 |
Class at
Publication: |
252/500 |
International
Class: |
H01B 1/12 20060101
H01B001/12 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 31, 2008 |
JP |
2008-090332 |
Claims
1. Display particles, which are used for an image display apparatus
having a structure in which the display particles in a powdered
state are sealed between two substrates at least one of which is
transparent, and by generating an electric field between the
substrates, the display particles are moved so that an image is
displayed, comprising: base particles A containing at least a resin
and a colorant, and having a volume-average particle size D1 of 1
to 50 .mu.m; resin fine particles B being externally added to the
base particles, and having an average primary particle size D2 of
30 to 250 nm; and inorganic fine particles C being externally added
to the base particles, and having an average primary particle size
D3 of 5 to 30 nm, wherein the display particles for an image
display apparatus are designed so that D1, D2 and D3 satisfy the
following formulae: 10.ltoreq.D1/D2.ltoreq.1000 (1)
2.ltoreq.D2/D3.ltoreq.50 (2).
2. The display particles of claim 1, wherein the resin fine
particles B is contained at a content of 0.1 to 200 parts by weight
relative to 100 parts by weight of the base particles.
3. The display particles of claim 1, wherein the inorganic fine
particles C is contained at a content of 0.01 to 30 parts by weight
relative to 100 parts by weight of the base particles.
4. The display particles of claim 1, wherein the display particles
comprise positively charged display particles and negatively
charged display particles, with any of the display particles being
formed of the base particles A to which the resin fine particles B
and the inorganic fine particles B are externally added.
5. An image display apparatus comprising the display particles of
claim 1.
6. The display particles of claim 2, wherein the inorganic fine
particles C is contained at a content of 0.01 to 30 parts by weight
relative to 100 parts by weight of the base particles.
7. The display particles of claim 2, wherein the display particles
comprise positively charged display particles and negatively
charged display particles, with any of the display particles being
formed of the base particles A to which the resin fine particles B
and the inorganic fine particles B are externally added.
8. The display particles of claim 3, wherein the display particles
comprise positively charged display particles and negatively
charged display particles, with any of the display particles being
formed of the base particles A to which the resin fine particles B
and the inorganic fine particles B are externally added.
9. An image display apparatus comprising the display particles of
claim 2.
10. An image display apparatus comprising the display particles of
claim 3.
11. An image display apparatus comprising the display particles of
claim 4.
Description
[0001] This application is based on application(s) No. 2008-090332
filed in Japan, the contents of which are hereby incorporated by
reference.
TECHNICAL FIELD
[0002] The present invention relates to an image display apparatus
capable of displaying and erasing images repeatedly by moving
display particles in an electric field, and to display particles to
be used in the image display apparatus.
BACKGROUND ART
[0003] Conventionally, an image display apparatus has been known in
which an image is displayed by moving display particles in a
gaseous phase. This image display apparatus has a structure in
which the display particles in a powdered state are sealed between
two substrates at least one of which is transparent, and by
generating an electric field between the substrates, the display
particles are moved and adhered to one of the substrates so that an
image is displayed. Upon driving such an image display apparatus, a
voltage is applied between the substrates to generate an electric
field so that the display particles are moved in the electric field
direction; therefore, by selecting appropriately the direction of
the electric field, a displaying operation and an erasing operation
of an image can be carried out repeatedly. For this reason, in the
image display apparatus, there have been demands for moving the
display particles smoothly even under a low driving voltage.
[0004] However, once the display particles have been adhered to the
substrate, the adhesive strength is comparatively strong;
therefore, in an attempt to carry out image displaying and erasing
operations repeatedly, a high voltage has to be applied between the
substrates so as to separate the adhered display particles
therefrom. When the number of display particles that have been left
adhered to the substrate surface increases, the density of a
display image is lowered to cause a reduction in the contrast of
the image and affect in the image quality. These problems of an
increase in the driving voltage and a reduction in the contrast
tend to become conspicuous as the image display apparatus is used
repeatedly.
[0005] Consequently, in order to reduce the adhesive strength
between the display particles and the substrate, a technique has
been known in which fine particles of silica, titanium oxide or the
like, having, for example, an average primary particle size of 5 to
50 nm, are externally added to the display particles (for example,
Patent Literature 1.
[0006] Citation List
[0007] Patent Literature 1: Japanese Patent Laid-Open No.
2004-29699
SUMMARY OF INVENTION
Technical Problem
[0008] However, the above-mentioned technique cannot provide a
sufficient adhesive strength-reducing effect, resulting in a
failure to sufficiently achieve a low-voltage operation (100V or
less).
[0009] An object of the present invention is to provide display
particles for an image display apparatus that can display an image
having comparatively high contrast repeatedly even when a driving
voltage is comparatively low, and an image display apparatus
provided with such display particles.
Solution to Problem
[0010] The present invention provides to display particles, which
are used for an image display apparatus having a structure in which
the display particles in a powdered state are sealed between two
substrates at least one of which is transparent, and by generating
an electric field between the substrates, the display particles are
moved so that an image is displayed, include:
[0011] base particles A containing at least a resin and a colorant,
and having a volume-average particle size D1 of 1 to 50 .mu.m;
[0012] resin fine particles B being externally added to the base
particles, and having an average primary particle size D2 of 30 to
250 nm; and
[0013] inorganic fine particles C being externally added to the
base particles, and having an average primary particle size D3 of 5
to 30 nm, in which the display particles for an image display
apparatus are designed so that D1, D2 and D3 satisfy the following
formulae:
10.ltoreq.D1/D2.ltoreq.1000 (1)
2.ltoreq.D2/D3.ltoreq.50 (2)
and to an image display apparatus provided with such display
particles.
ADVANTAGEOUS EFFECTS OF INVENTION
[0014] In accordance with the present invention, since an adhesive
strength-reducing effect is improved by fine particles (external
additives) to be externally added to the display particles, it
becomes possible to display an image having comparatively high
contrast repeatedly even when a driving voltage is comparatively
low.
BRIEF DESCRIPTION OF DRAWINGS
[0015] FIG. 1 is a schematic view showing one example of display
particles for an image display apparatus.
[0016] FIG. 2 is a schematic view showing one example of a
cross-sectional structure of the image display apparatus.
[0017] FIG. 3 is a schematic view showing an example of movements
of the display particles upon application of a voltage between
substrates.
[0018] FIG. 4 is a schematic view showing an example of movements
of the display particles upon application of a voltage between
substrates.
[0019] FIG. 5 is a schematic view showing an example of a shape of
an image display surface.
[0020] FIG. 6 is a schematic view showing one example of a sealing
method for the display particles.
DESCRIPTION OF EMBODIMENTS
[0021] The present invention relates to display particles, which
are used for an image display apparatus having a structure in which
the display particles in a powdered state are sealed between two
substrates at least one of which is transparent, and by generating
an electric field between the substrates, the display particles are
moved so that an image is displayed, include:
[0022] base particles A containing at least a resin and a colorant,
and having a volume-average particle size D1 of 1 to 50 .mu.m;
[0023] resin fine particles B being externally added to the base
particles, and having an average primary particle size D2 of 30 to
250 nm; and
[0024] inorganic fine particles C being externally added to the
base particles, and having an average primary particle size D3 of 5
to 30 nm, in which the display particles for an image display
apparatus are designed so that D1, D2 and D3 satisfy the following
formulae:
10.ltoreq.D1/D2.ltoreq.1000 (1)
2.ltoreq.D2/D3.ltoreq.50 (2)
and to an image display apparatus provided with such display
particles.
[0025] Display Particles for an Image-Forming Apparatus
[0026] Display particles for an image-display apparatus
(hereinafter, referred to simply as "display particles") according
to the present invention contain base particles A, resin fine
particles B and inorganic fine particles C, and specifically resin
fine particles B and inorganic fine particles C are externally
added to base particles A. Impurities may be contained as far as
the effects of the present invention are not ruined. The display
particles normally contain positively charged display particles and
negatively charged display particles, and each of the display
particles has the structure in which resin fine particles B and
inorganic fine particles C are externally added to base particles
A. The positively charged display particles and the negatively
charged display particles are charged to predetermined polarities
by, for example, being made in friction-contact with each other, or
by being made in friction-contact with a reference material such as
iron particles (carrier) serving as a charge-applying material. The
charging polarities can be controlled by, for example, the kinds of
a resin and a charge-controlling agent to be contained in the base
particle or the kinds of an external additive to be externally
added thereto, or the like.
[0027] The base particles play following roles.
[0028] (1) The base particles contain a colorant and have an
appropriate size, and thereby function to express color for
display.
[0029] (2) The base particles have been electrical charged and move
by Coulomb force caused by an applied electrical field. Thereby,
the base particles function to change the display color.
[0030] (3) The base particles have an appropriate adhesive strength
(Van der Waals force+liquid cross-linking force+image force).
Thereby, the base particles function to keep the display color as
they are when the power supply is turned off.
[0031] Base particles A are colored resin particles containing at
least a resin and a colorant, and different colored colorants are
contained between base particles A1 contained in the positively
charged display particles and base particles A2 contained in the
negatively charged display particles. When simply referred to as
base particles A, this means the base particles A1 as well as the
base particles A2 inclusively.
[0032] The term "different colors" means that, when an electric
field is generated between substrates in an image-displaying
apparatus that will be described later, a displayed image can be
visually recognized by differences such as in color phase,
brightness and chromaticness between display particles that are
moved and allowed to adhere onto the substrate on the upstream side
in the visually recognizing direction and display particles that
are left and allowed to adhere onto the substrate on the downstream
side in the visually recognizing direction. For example,
white-color base particles and black-color base particles are used
in combination.
[0033] The colors can be controlled by the kinds of the colorant
contained in the base particles (black: carbon black, iron oxide,
and aniline black; white: titanium oxide, zinc oxide, and zinc
sulfide).
[0034] The resin that forms the base particles A is not
particularly limited, and typical examples thereof are the
following polymers referred to as vinyl-based resins, and in
addition to the vinyl-based resins, condensation-type resins, such
as a polyamide resin, a polyester resin, a polycarbonate resin and
an epoxy resin may be included. Specific examples of the
vinyl-based resins include a polystyrene resin, a polyacrylic resin
and a polymethacrylic resin, and in addition to these, a polyolefin
resin formed by an ethylene monomer and a propylene monomer or the
like may be included. As resins other than the vinyl-based resin,
in addition to the condensation-type resins, a polyether resin, a
polysulfone resin, a polyurethane resin, a fluorine-based resin, a
silicone-based resin and the like may be included.
[0035] The polymer constituting a resin that is usable for the base
particles A may be obtained by using at least one kind of
polymerizable monomers that form these resins, and in addition to
these, the polymer may also be produced by combining plural kinds
of polymerizable monomers. Upon producing a resin by combining
plural kinds of polymerizable monomers, for example, methods for
forming copolymers, such as a block copolymer, a graft copolymer
and a random copolymer, may be used, and in addition to these,
there is also a resin forming method, such as a polymer blending
method in which plural kinds of resins are mixed with one
another.
[0036] The base particles that contain, for example, a
styrene-acrylic-based resin, an acrylic-based resin or a
fluorine-based resin among the above-mentioned resins tend to be
charged with a negative polarity; therefore, the base particles are
useful for negatively charged display particles. The base particles
that contain, for example, a polyamide-based resin or a
polymethacrylic resin tend to be charged with a positive polarity;
therefore the base particles are useful for positively charged
display particles.
[0037] The weight-average molecular weight of a resin constituting
the base particles A is 5000 to 200000, particularly preferably
15000 to 100000 from the viewpoint of easily fixing the resin
particles B.
[0038] In the present specification, the weight-average molecular
weight is a value measured by a HLC-8220 (made by Tosoh
Corporation).
[0039] Not particularly limited, pigments conventionally known in
the field of the electrophotographic toner can be used as a
colorant. Among these, examples of a white pigment constituting the
white base particles include zinc oxide (zinc white), titanium
oxide, antimony white, zinc sulfide, barium titanate, calcium
titanate, strontium titanate or the like, and among these, titanium
oxide is preferable. Examples of a black pigment constituting the
black base particles include carbon black, copper oxide, manganese
dioxide, aniline black, active carbon or the like, and among these,
carbon black is preferable. Although not particularly limited, the
content of the colorant may be, for example, 1 to 200 parts by
weight relative to 100 parts by weight of the resin.
[0040] A charge controlling agent conventionally used in the field
of the electrophotographic toner may be contained in the base
particles A on demand.
[0041] Not particularly limited, charge controlling agents
conventionally known in the field of the electrophotographic toner
may be used as a charge controlling agent. Among these, base
particles containing a negative-charge controlling agent, such as,
for example, a salicylic acid metal complex, a metal-containing azo
dye, a quaternary ammonium salt compound and a nitroimidazole
derivative, are useful as negatively charged display particles.
Base particles containing a positive-charge controlling agent, such
as, for example, a nigrosine-based dye, a triphenylmethane compound
and an imidazole derivative, are useful as positively charged
display particles. Although not particularly limited, the content
of the charge controlling agent may be, for example, 0.1 to 10
parts by weight relative to 100 parts by weight of the resin.
[0042] The volume-average particle size D1 of the base particles A
is 1 to 50 .mu.m, and preferably 1 to 30 .mu.m. In the case where
positively charged display particles and negatively charged display
particles are used, supposing that the volume average particle size
of the entire base particles of the base particles A1 for
positively charged display particles and base particles A2 for
negatively charged display particles is D1, and the value may be
set within the above-mentioned range. When D1 is too small, the Van
der Waals force increases to cause the display particles to
mutually aggregate with one another, resulting in reduction in
contrast. On the other hand, when D1 is too large, the stress upon
driving increases because of the self-weight of the particles to
cause embedded external additives, with the result that the
repeatability deteriorates.
[0043] The volume-average particle size D1 of the base particles is
indicated by a volume based median diameter (d50 diameter), and can
be measured and calculated by using a device in which a
data-processing computer system is connected to a Multisizer 3
(made by Beckman Coulter, Inc.).
[0044] The measurement procedures are described as follows: After a
sample (0.02 g) has been properly mixed with a surfactant solution
(20 ml) (used for dispersing particles; a surfactant solution
prepared by diluting a neutral detergent containing a surfactant
component by 10 times with pure water), this is dispersed by using
ultrasonic waves for one minute so that a dispersion solution is
prepared. This dispersion solution is injected into a beaker,
inside a sample stand, which contains ISOTON II (made by Beckman
Coulter, Inc.), by using a pipet, until a measured concentration of
10% is attained, and measurements are carried out with the
measuring device counter being set to 2500. The multisizer 3 in
which the aperture diameter is set to 5 .mu.m is used.
[0045] The method for producing the base particles is not
particularly limited, and conventionally known methods for
producing particles containing a resin and a colorant, such as, for
example, a method for producing toner to be used for forming images
in an electrophotographic system, may be applied to be used.
Specific methods for producing the base particles include, for
example, the following methods.
[0046] (1) a method in which, after a resin and a colorant are
mixed and kneaded with each other, the resulting kneaded matter is
subjected to each of pulverizing and classifying processes so that
base particles are produced;
[0047] (2) a so-called suspension polymerizing method in which,
after a polymerizable monomer and a colorant are mechanically
stirred in an aqueous medium to form droplets, a polymerizing
process is carried out so that base particles are produced; and
[0048] (3) a so-called emulsion polymerizing aggregation method in
which a polymerizable monomer is dropped into an aqueous medium
containing a surfactant so that a polymerizing reaction is carried
out in a micelle to produce polymer particles of 100 to 150 nm, and
then colorant particles and a coagulant are added thereto so that
these particles are aggregated and fused to produce base
particles.
[0049] The resin fine particles B play following roles.
[0050] (1) The resin fine particles are mainly fixed on the surface
of the base particle, resulting in that such a situation as if the
irregularity is formed on the surface of the base particle is
expressed. Thereby, resin fine particles function to form fine
spaces between the base particle and the substrate (spacer
effect).
[0051] The resin fine particles work to reduce an interaction
caused by the contact of display particles with the substrate. In
more particular, Van der Waals force and image force are
deteriorated, resulting in reduction in the adhesive force between
the display particles and the substrate, and improvement of
contrast at lower driving voltage.
[0052] (2) The resin fine particles themselves are fixed to the
base particles and work to fix inorganic fine particles to the base
particles. In other words, the resin fine particles function as an
adhesive to bond the inorganic fine particles to the base
particles.
[0053] The resin fine particles B have an average primary particle
size D2 of 30 to 250 nm, preferably 50 to 200 nm, and satisfy the
following formula (1) in association with D1 of the base particles
A. The value of D1/D2 is a value obtained by converting D1 and D2
to the same unit so as to be calculated.
10.ltoreq.D1/D2.ltoreq.1000, preferably 50.ltoreq.D1/D2.ltoreq.300
(1)
[0054] In the case where positively charged display particles and
negatively charged display particles are used, supposing that the
average primary particle size of the entire resin fine particles of
the resin fine particles B1 contained in positively charged display
particles and the resin fine particles B2 contained in negatively
charged display particles is D2, the value may be set within the
above-mentioned range, and allowed to satisfy the above-mentioned
formula (1) in association with D1. When D2 is too small, the space
effect provided by the resin fine particles B becomes smaller,
failing to provide a sufficient contrast at low voltages. When D2
is too large, the resin fine particles B are hardly fixed onto the
base particles, and allowed to be present in an isolated state,
with the result that the effect is not obtained. In the case where
D1/D2 is too small, since the base particles A are not uniformly
coated with the resin particles B, the effect is not obtained. In
the case where D1/D2 is too large, since the resin particles B are
buried into the base particles A upon carrying out an externally
adding process, with the result that the effect is not obtained.
When referred to simply as "resin fine particles B", it means the
resin fine particles B1 and B2 inclusively.
[0055] The average primary particle size of the resin fine
particles B is a number-average particle size of primary particles,
and the number-based median diameter (d50 diameter) is obtained by
using a value measured by a micro track UPA-150 (made by Nikkisou
Co., Ltd.).
[0056] The measurements procedures are described as follows: To a
measuring cylinder of 50 ml are put resin fine particles (0.1 g) to
be measured, and to this is added 25 ml of pure water, and the
resulting mixture is dispersed by using an ultrasonic washer "US-1
(AS ONE CORPORATION)" for 3 minutes so that a test sample is
prepared. The test sample (3 ml) is then charged into a cell of a
"micro track UPA-150" so that the value of "Sample Loading" is
confirmed to be in the range between 0.1 to 100. Then, measurements
are carried out under the following conditions.
Measuring Conditions
[0057] Transparency: Yes
[0058] Refractive Index: 1.59
[0059] Particle Density: 1.05 g/cm.sup.3
[0060] Spherical Particles Yes
Solvent Conditions
[0061] Refractive Index: 1.33
[0062] Viscosity: High (temp) 0.797.times.10-3 Pas
[0063] Low (temp) 1.002.times.10-3 Pas
[0064] The resin constituting the resin fine particles B is not
particularly limited, and, for example, the resin exemplified as a
resin for constituting the base particles A may be used.
[0065] The glass transition point (Tg) of the resin constituting
the resin fine particles B is 40 to 200.degree. C., and
particularly preferably 50 to 100.degree. C., from the viewpoint of
fixing onto the base particles A.
[0066] In the present specification, Tg is obtained by using a
value measured by a DSC-7 Differential Scanning Calorimeter (made
by Parkin-Elmer Co., Ltd.).
[0067] The content of the resin fine particles B is 0.1 to 200
parts by weight, and particularly preferably 1 to 20 parts by
weight, relative to 100 parts by weight of the base particles to
which the resin fine particles are externally added, in order to
reduce contact points between the display particles and the
substrate and also to reduce the adhesive force exerted between the
particles and the substrate. The resin fine particles B may be used
in combination of two or more kinds, and in this case, the total
amount of these may be within the above-mentioned range. In the
case where positively charged display particles and negatively
charged display particles are used, the contents of the resin fine
particles B1/B2 are set so that respective values relative to 100
parts by weight of the base particles A1/A2 are preferably set
within the above-mentioned range.
[0068] The inorganic fine particles C play following roles.
[0069] The inorganic fine particles are fixed mainly to the resin
fine particles and function as contact points between the substrate
and the display particles. In a manner similar to the resin fine
particles, the inorganic fine particles effectuate to express such
a situation as if the irregularity is formed on the surface of the
resin fine particle. Thereby, inorganic fine particles function to
form fine spaces between the display particles and the substrate
(spacer effect). Similarly, Van der Waals force and image force are
deteriorated. In a preferred embodiment, the surface of the
inorganic fine particle is subjected to a hydrophobicizing
treatment. Thereby, because the liquid cross-linking force, which
is an interaction caused by absorbed water, is further reduced, the
adhesive force between the display particles and the substrate are
reduced, resulting in improvement of contrast at lower driving
voltage.
[0070] The inorganic fine particles C have an average primary
particle size D3 of 5 to 30 nm, preferably 5 to 20 nm, and satisfy
the following formula (2) in association with D2 of the resin fine
particles B. The value of D2/D3 is a value obtained by converting
D2 and D3 to the same unit so as to be calculated.
2.ltoreq.D2/D3.ltoreq.50, preferably 5.ltoreq.D2/D3.ltoreq.20
(2)
[0071] In the case where positively charged display particles and
negatively charged display particles are used, supposing that the
average primary particle size of the entire inorganic fine
particles of the inorganic fine particles C1 contained in the
positively charged display particles and the inorganic fine
particles C2 contained in negatively charged display particles is
D3, the value may be set within the above-mentioned range, and
allowed to satisfy the above-mentioned formula (2) in association
with D2. When D3 is too small, the Van der Waals force between
particles increases so that the particles are not broken upon
carrying out the externally applying process, with the result that
the inorganic fine particles C are present as aggregates, failing
to provide the effect. When D3 is too large, the inorganic fine
particles C are hardly fixed onto the resin fine particles B, and
allowed to be present in an isolated state, with the result that
the effect is not obtained. In the case where D2/D3 is too small,
since the resin particles B are not uniformly coated with the
inorganic fine particles C, the effect is not obtained. In the case
where D2/D3 is too large, since the inorganic fine particles C are
buried into the resin particles B upon carrying out an externally
adding process, with the result that the effect is not obtained.
When referred to simply as "inorganic fine particles C", it means
the inorganic fine particles C1 and C2 inclusively.
[0072] The average primary particle size of the inorganic fine
particles C is a number-average particle size of primary particles
(number-based median diameter (d50 diameter)), and calculated from
an image photographed by a scanning type electron microscope.
[0073] The measurement procedures are described as follows: A
photograph of particles, magnified by 100000 times, is photographed
by a scanning-type electron microscope "JSM-7410" (made by JEOL
LTD.), and with respect to each of the 200 particles, the largest
length (the largest length between arbitrary two points on the
circumference of each particle) is measured so that the
number-average value thereof is defined as the average particle
size. In the case where the particles are photographed as
aggregates, the particle size of the primary particles forming each
aggregate is supposed to be measured.
[0074] Although not particularly limited, examples of materials
useable as the inorganic fine particles C include: metal oxides,
such as silicon oxide, titanium oxide, aluminum oxide, tin oxide,
zirconium oxide and tungsten oxide, nitrides such as titanium
nitride, and titanium compounds, and silicon oxide is preferable
because it provides a high degree of hydrophobicity.
[0075] From the viewpoint of reducing a liquid cross-linking force
between the particles and the substrate, the inorganic fine
particles C is preferably allowed to have a hydrophobic property.
The hydrophobic property is imparted by treating the inorganic fine
particles with a hydrophobicizing agent. Not particularly limited,
examples of the hydrophobicizing agent also include any of silane
coupling agents, such as chlorosilane, alkoxysilane, silazane,
aminosilane and silylated isocyanate. Specific examples include:
such as dimethyl dichlorosilane, trimethyl chlorosilance,
methylmethoxy silane, isobutyltrimethoxy silane, hexamethyl
disilazane, tert-butyldimethylchlorosilane, vinyltrichlorosilane,
vinyltrimethoxysilane, vinyltriethoxysilane,
isopropyl-tri(N-aminoethyl-aminoethyl) titanate,
aminopropyltrimethoxy silane, aminopropyltriethoxy silane,
dimethylaminopropyltrimethoxy silane, diethylaminopropyl trimethoxy
silane, dipropylaminopropyltrimethoxy silane,
dibutylaminopropyltrimethoxy silane, monobutylaminopropyltrimethoxy
silane, dioctylaminopropyldimethoxy silane,
dibutylaminopropyldimethoxy silane, dibutylaminopropylmonomethoxy
silane, dimethylaminophenyl triethoxy silane,
(N-(2-aminoethyl)-3-aminopropyltrimethoxy silane),
(3-trimethoxysilylpropyl) diethylenetriamine,
bis[3-(trimethoxysilyl)propyl] ethylenediamine,
trimethoxysilyl-.gamma.-propylphenylamine and
trimethoxysilyl-.gamma.-propylbenzylamine.
[0076] The inorganic fine particles C preferably exhibit a degree
of hydrophobicity of 30 to 99.
[0077] The degree of hydrophobicity is obtained by using a value
measured based upon methanol wettability. The methanol wettability
is a factor used for evaluating the wettability to methanol. In
this method, 0.2 g of inorganic fine particles to be measured are
weighed and added to 50 ml of distilled water put in a beaker
having an inner volume of 200 ml. Methanol is slowly dropped
therein from a burette with its tip being immersed in the solution,
while being slowly stirred, until the entire inorganic fine
particles are moistened. Supposing that the amount of methanol
required for completely moistening the inorganic fine particles is
the value of "a" (ml), the degree of hydrophobicity is calculated
from the following equation:
Degree of hydrophobicity={a/(a+50)}.times.100
[0078] From the viewpoint of providing flowability, the content of
the inorganic fine particles C is 0.01 to 30 parts by weight, and
particularly preferably 0.1 to 5 parts by weight relative to 100
parts by weight of the base particles to which the inorganic fine
particles are externally added. Two or more kinds of the inorganic
fine particles C may be used in combination, and in this case, the
total amount of these may be set in the above-mentioned range. In
the case where positively charged display particles and negatively
charged display particles are used, the contents of the inorganic
fine particles C1/C2 are set so that respective values relative to
100 parts by weight of the base particles A1/A2 are preferably set
within the above-mentioned range.
[0079] The display particles of the present invention can be
produced by adding the resin fine particles B and the inorganic
fine particles C to the base particles A to be mixed (production
method 1), and preferably, they are produced by processes in which
after the resin fine particles B are added to the base particles A
to be mixed, the inorganic fine particles C are added to the
mixture to be mixed (production method 2). In particular, in the
case where display particles containing positively charged display
particles and negatively charged display particles are used, the
above-mentioned production method 1, preferably, production method
2, is adopted upon producing the respective display particles. In
the production method, as wn in FIG. 1, a display particle having a
two-stage lamination structure in which the surface of the base
particle A(1) is coated with the resin fine particles B(2), with
the surface of the resin fine particle B(2) being coated with the
inorganic fine particles C(3), is obtained. The display particles
having such a structure make it possible to reduce contact points
between the particles and the substrate by coating the base
particle A with the resin fine particles B, and furthermore to
reduce a liquid cross-linking force between the particles and the
substrate by coating the surface of the resin fine particle B with
the inorganic fine particles C that is subjected to a
hydrophobicizing treatment. As a result, since the adhesive
strength of the display particles to the substrate is effectively
reduced, images having comparatively high contrast can be displayed
repeatedly even when the driving voltage is comparatively low.
[0080] In the above-mentioned two-stage lamination structure, the
resin fine particles B are preferably fixed to the base particle A,
and the inorganic fine particles C are preferably fixed to resin
fine particles B. Thus, the above-mentioned effects can be obtained
for a long period of time. For this reason, in the method for
producing display particles, after the resin fine particles B are
added to and mixed with the base particles A and inorganic fine
particles C are added to and mixed with the mixture, the resulting
mixture is preferably subjected to an instantaneous heating
treatment. By using the instantaneous heating treatment, the fixing
of the resin fine particles B to the base particles A and the
fixing of the inorganic fine particles C to the resin fine
particles B can be effectively carried out. The "fixing" is used as
a concept including a phenomenon in which some portions of the
resin fine particles B and the inorganic fine particles C are
buried in the base particle A to be fixed thereto and a phenomenon
in which some portions of the inorganic fine particles C are buried
in the resin fine particles B to be fixed thereto, between
different types of particles (between the base particles A and the
resin fine particles B and the inorganic fine particles C, and
between the resin fine particles B and the inorganic fine particles
C).
[0081] The instantaneous heating treatment refers to a heating
treatment in which hot air is instantaneously blown to a substance
to be treated. The heating temperature may be such a temperature as
to achieve the above fixation and not to cause complete burying of
the particles and fusing between the same kind of particles, and
determined depending on, for example, the weight-average molecular
weight of the base particles A, Tg of the resin fine particles B
and the like. Specifically, in the case where the weight-average
molecular weight of the base particles A is about 5000 to 200000,
with Tg of the resin fine particles B being about 40 to 200.degree.
C., the heating temperature is appropriately normally 80 to
300.degree. C. As the device capable of carrying out such an
instantaneous heating treatment, a commercially available hot-air
spherizing device (Surfusing System SFS-3; made by Nippon Pneumatic
MFG.) may be used.
[0082] The fixing rates of the resin fine particles B and the
inorganic fine particles C in the display particles of the present
invention are 50 to 99%, and particularly preferably 70 to 99%. In
the case where positively charged display particles and negatively
charged display particles are used, the above-mentioned fixing rate
is preferably achieved in the entire display particles.
[0083] The above-mentioned fixing rate can be measured by
determining the remaining rate of the resin fine particles B and
the inorganic fine particles C when vibration is applied to the
display particles. Specifically, a measuring method, which executes
a first step for measuring the BET specific surface area (initial
value) of the display particles, a second step for applying
ultrasonic waves to the display particles in water and a third step
for measuring the BET specific surface area (value after the
process) of residues of the display particles from which free resin
fine particles B and inorganic fine particles C are removed after
the application of ultrasonic waves, may be adopted. With respect
to the BET specific surface area, a proportion of value after the
process relative to the initial value is calculated, and the
resulting value (remaining rate) is defined as a fixing rate. The
reason that the value is considered as the fixing rate is because,
since the particle size of the base particle A is extremely large
in comparison with those of the resin fine particles B and the
inorganic fine particles C, the surface area of the base particle A
is extremely small in comparison with those of the resin fine
particles B and the inorganic fine particles C so that it is
negligible.
[0084] Image Display Apparatus
[0085] The image display apparatus in accordance with the present
invention is characterized by including the above-mentioned display
particles. The image display apparatus of the present invention is
explained in detail hereinafter. The image display apparatus
according to the present invention is referred to also as "powder
display".
[0086] The image display apparatus according to the present
invention has a structure in which the above-mentioned display
particles in a powdered state are sealed between two substrates at
least one of which is transparent, and by generating an electric
field between the substrates, the display particles are moved so
that an image is displayed.
[0087] FIG. 2 shows a typical structural cross section of the image
display apparatus in accordance with the present invention. FIG.
2(a) shows a structure in which electrodes 15 having a layer
structure are provided on substrates 11 and 12, with an insulating
layer 16 being provided on the surface of the electrodes 15. The
image display apparatus of FIG. 2(b) has a structure in which no
electrodes are provided inside the apparatus, and an electric field
is applied thereto through electrodes provided on the outside of
the apparatus so that the display particles can be moved. In FIGS.
2(a) and 2(b), the same members are indicated by the same reference
numerals. FIG. 2 is supposed to indicate FIGS. 2(a) and 2(b)
inclusively. As shown in the Figures, an image display apparatus 10
of FIG. 2 is supposed to allow images to be visually recognized
from the substrate 11 side; however, the present invention is not
intended to be limited by the structure in which images are
visually recognized from the substrate 11 side. In the apparatus
type shown in FIG. 2(b), since no electrodes 15 are provided in the
apparatus itself, the structure of the apparatus can be simplified
so that the advantage of shortening the manufacturing processes can
be obtained. FIG. 4 shows a state in which the image display
apparatus 10 of the type shown in FIG. 2(b) is set to a device
capable of applying a voltage, with a voltage being applied
thereto. The cross-sectional structure of the image display
apparatus according to the present invention is not intended to be
limited by those structures shown in FIGS. 2(a) and 2(b).
[0088] Two substrates 11 and 12 that are a case member constituting
the image display apparatus are disposed face to face with each
other on the outermost portion of the image display apparatus 10 of
FIG. 2(a). On the surfaces on the side where the paired substrates
11 and 12 are made face to face with each other, electrodes 15 used
for applying a voltage are provided, with insulating layers 16
being furthermore provided on the electrodes 15. The electrodes 15
and the insulating layers 16 are respectively provided on the
substrate 11 and the substrate 12, and display particles are
located in a gap 18 formed by making the surfaces on the side
having the electrodes 15 and the insulating layers 16 face to face
with each other. In the image display apparatus 10 shown in FIG. 2,
two kinds of display particles, that is, black display particles
(hereinafter, referred to as black particles) 21 and while display
particles (hereinafter, referred to as white particles) 22 are
placed in the gap 18 as the display particles. The aforementioned
resin fine particles and inorganic fine particles are externally
added to and present on the surface of each black particle 21 and
each white particle 22; however, these are not shown. In the image
display apparatus 10 of FIG. 2, the gap 18 is surrounded from four
sides by the substrates 11 and 12 and two partition walls 17, and
the display particles are located in the gap 18 in a sealed
state.
[0089] The thickness of the gap 18 is not particularly limited as
long as it allows the sealed display particles to move and can
maintain the contrast of an image, and is normally 10 .mu.m to 500
.mu.m, preferably 1 .mu.m to 100 .mu.m. The volume occupation rate
of the display particles inside the gap 18 is 5% to 70%, preferably
30% to 60%. By setting the volume occupation rate of the display
particles in the above-mentioned range, the display particles are
allowed to move smoothly in the gap 18, and further, an image with
superior contrast can be obtained.
[0090] The behaviors of the display particles in the gap 18 of the
image display apparatus 10 is explained hereinafter.
[0091] In the image display apparatus in accordance with the
present invention, when a voltage is applied between the two
substrates to form an electric field, the charged display particles
are allowed to move along the electric field direction. In this
manner, by applying a voltage between the substrates where the
display particles are present, the charged display particles move
between the substrates so that an image is displayed.
[0092] The image displaying operations in the image display
apparatus of the present invention is carried out as the following
procedures:
[0093] (1) The display particles used as display media are charged
by using a known method, such as frictional charging by the use of
carriers.
[0094] (2) The display particles are sealed between the two
opposing substrates, and in this state, a voltage is applied
between the substrates.
[0095] (3) By the application of a voltage between the substrates,
an electric field is formed between the substrates.
[0096] (4) The display particles are attracted toward the substrate
surface along the electric field direction opposite to the polarity
of the display particles due to a function of the force of the
electric field between the electrodes to carry out image
displaying.
[0097] (5) The moving directions of the display particles are
switched by changing the electric-field direction between the
substrates. The image display can be changed variously by switching
the moving directions.
[0098] Examples of the charging method for display particles by the
above-mentioned conventional method include such as a method for
charging the display particles through frictional charging by
allowing them to contact with carriers and a method for mixing and
stirring display particles with two colors having different
charging polarities so that the display particles are charged
through frictional charging between the two particles, and in the
present invention, a method in which the carriers are used for
charging the display particles, and the charged display particles
are sealed between the substrates is preferably used.
[0099] FIGS. 3 and 4 show examples of the movements of the display
particles with an application of a voltage between the
substrates.
[0100] FIG. 3(a) shows a state prior to the application of the
voltage between the substrates 11 and 12, and prior to the
application of the voltage, the white particles 22 positively
charged are present near the substrate 11 on the image-visible
side. In this state, a white image is displayed on the image
display apparatus 10. FIG. 3(b) shows a state after the application
of the voltage to the electrodes 15 in which negatively charged
black particles 21 due to the application of a positive voltage to
the substrate 11 are allowed to move close to the substrate 11 on
the image-visible side, with the white particles 22 moving toward
the substrate 12 side. In this state, a black image is displayed on
the image display apparatus 10.
[0101] FIG. 4 shows a state in which an image display apparatus 10
of the type having no electrodes, shown in FIG. 2(b), is set to a
voltage application device 30, and in this state, a state prior to
an application of a voltage (FIG. 4(a)) and a state after the
application of the voltage (FIG. 4(b)) are shown. In the same
manner as in the image display apparatus 10 having the electrodes
15, the image display apparatus 10 of the type shown in FIG. 2(b)
also has a structure in which by applying a positive voltage to the
substrate 11, the negatively charged black particles 21 are allowed
to move close to the substrate 11 on the image-visible side, with
the white particles 22 moving toward the substrate 12 side.
[0102] The following description is about the substrates 11 and 12,
electrodes 15, insulating layer 16 and partition walls 17 that
constitute the image display apparatus 10 shown in FIG. 2.
[0103] First, the substrates 11 and 12 constituting the image
display apparatus 10 are explained. In the image display apparatus
10, since a viewer visually recognizes an image formed by the
display particles from at least one of the sides of the substrates
11 and 12, the substrate on the side through which the viewer
recognizes the image needs to be made from a transparent material.
Therefore, the substrate to be used for the side through which the
viewer recognizes the image is preferably made from a
light-transmitting material having, for example, a visible light
transmittance of 80% or more, and by providing the visible light
transmittance of 80% or more, it is possible to obtain sufficient
visibility. Of the substrates forming the image display apparatus
10, the substrate placed on the side opposite to the
image-recognizing side does not need to be made from a transparent
material.
[0104] The thicknesses of the substrates 11 and 12 are preferably 2
.mu.m to 5 mm respectively, more preferably Sum to 2 mm. When the
thicknesses of the substrates 11 and 12 are within the
above-mentioned range, it is possible to provide a sufficient
strength for the image display apparatus 10, and also to maintain
the distance between the substrates uniformly. By setting the
thicknesses of the substrates within the above-mentioned range, it
becomes possible to provide a compact and light-weight image
display apparatus, and consequently to accelerate use of the image
display apparatus in wider fields. Furthermore, by setting the
thickness of the substrate on the image-recognizing side within the
above-mentioned range, the displayed image can be visually
recognized accurately, without causing any problems in display
quality.
[0105] Example of the material having a visible light transmittance
of 80% or more include inorganic materials having no flexibility,
such as glass and quartz, organic materials, typically represented
by resin materials to be described later, metal sheets, or the
like. Among these, the organic materials and metal sheets may
provide a certain degree of flexibility for the image display
apparatus. Examples of the resin materials capable of providing a
visible light transmittance of 80% or more include polyester resins
typically represented by such as polyethylene terephthalate and
polyethylene naphthalate, polycarbonate resins, polyether sulfone
resins, polyimide resins and the like. Acrylic resins that are
polymers of acrylates and methacrylates, typically represented by
polymethyl methacrylate (PMMA), and transparent resins obtained by
radical-polymerizing a vinyl-based polymerizable monomer, such as a
polyethylene resin, may also be included.
[0106] The electrodes 15 are provided on the surfaces of the
substrates 11 and 12, and used for forming an electric field
between the substrates, that is, in a gap 18, by application of a
voltage. In the same manner as in the aforementioned substrate, the
electrodes 15 that are transparent need to be provided on the
image-visible side by the viewer.
[0107] The thickness of the electrodes provided on the
image-visible side needs to be such a level as to ensure
conductivity and as not to cause problems with the light
transmitting property, and specifically, it is preferably 3 nm to 1
.mu.m, more preferably 5 nm to 400 nm. The visible light
transmittance of the electrodes to be provided on the image-visible
side is preferably set to 80% or more in the same manner as in the
substrate. The thickness of the electrode to be provided on the
side opposite to the image-visible side is also preferably within
the above-mentioned range; however, the electrode is not
necessarily required to be transparent.
[0108] Examples of the constituent material for the electrodes 15
include metal materials, conductive metal oxides, or conductive
polymer materials etc. Specific examples of the metal materials
include aluminum, silver, nickel, copper and gold, and specific
examples of the conductive metal oxides include indium-tin oxides
(ITO), indium oxides, antimony-tin oxides (ATO), tin oxides, zinc
oxides and the like. Examples of the conductive polymer materials
include polyaniline, polypyrrole, polythiophene, polyacetylene and
the like.
[0109] Examples of the method for forming the electrodes 15 on the
substrates 11 and 12 include a sputtering method, a vacuum vapor
deposition method, a chemical vapor deposition method (CVD method),
a coating method and the like upon providing film-shaped
electrodes. A method in which a conductive material is mixed with a
solvent or a binder resin and the resulting mixture is applied onto
the substrate to form electrodes may also be used.
[0110] The insulating layer 16 is designed to be provided on the
surface of the electrodes 15, with the display particles 21 and 22
being made in contact with the surface of the insulating layer 16;
however, it is not necessarily required to be provided. The
insulating layer 16 has a function for alleviating a change in the
quantity of charge by a voltage to be applied upon moving the
display particles 21 and 22. By using a resin having highly
hydrophobic property, or by providing irregularities thereon, its
physical adhesive strength to the display particles can be reduced
so that it is also allowed to have a function for reducing the
driving voltage. Examples of the material for forming the
insulating layer 16 are those materials that have an electrical
insulating property, can be formed into a thin film, and are also
transparent, if necessary. The insulating layer to be provided on
the image-visible side is preferably made to have a visible-light
transmittance of 80% or more, in the same manner as in the
substrate. Specific examples thereof include silicone resins,
acrylic resins polycarbonate resins and the like.
[0111] The thickness of the insulating layer 16 is preferably 0.01
.mu.m or more to 10.0 .mu.m or less. That is, when the thickness of
the insulating layer 16 is in the above-mentioned range, the
display particles 21 and 22 can be moved without the necessity of
applying a high voltage between the electrodes 15, and this
thickness is preferable because, for example, an image-displaying
operation can be carried out by using a voltage in the same level
applied upon forming an image by using an electrophoretic
method.
[0112] The partition walls 17, which ensure the gap 18 between the
upper and lower substrates, may be formed not only on the edge
portions of the substrates 11 and 12 as shown on the right side and
left side of the upper stage of FIG. 5, but also inside thereof, if
necessary. The width of the partition walls 17, in particular, the
thickness of the partition wall on the image display face 18a side,
is desirably made as thin as possible from the viewpoint of
ensuring the clearness of a display image, for example, as shown on
the right side of the upper stage of FIG. 5.
[0113] The partition walls 17 to be formed inside the substrates 11
and 12 may be formed continuously, or may be formed intermittently,
in the surface and rear surface direction in the Figure on the
right side as well as on the left side on the upper stage of FIG.
5.
[0114] By controlling the shape and the arrangement of the
partition walls 17, cells to be placed between the gap 18 and
separated by the partition walls 17 can be disposed with various
shapes. Examples of the shapes and arrangement of the cells,
obtained when the gap 18 is viewed in the visually recognizable
direction of the substrate 11, are shown in a lower-stage drawing
of FIG. 5. As shown in the lower-stage drawing of FIG. 5, a
plurality of cells may be arranged in a honeycomb pattern or a
net-work pattern, with a shape, such as a square shape, a
triangular shape, a line shape, a round shape and a hexagonal
shape.
[0115] The partition walls 17 can be formed by processing the
surface of the substrate on the side opposite to the image-visible
side by using, for example, the following methods. Examples of the
methods for forming the partition walls 17 include such as a
concave/convex pattern forming process by using an emboss
processing and a thermal press-injection molding with a resin
material or the like, as well as a photolithographic method and a
screen printing method.
EXAMPLES
Example 1
Production of White Display Particles
[0116] (White Base Particles)
[0117] The following resin and titanium oxide were charged into a
Henschel mixer (made by Mitsui Miike Mining Co., Ltd.), and mixed
for 5 minutes, with a peripheral velocity of stirring blades being
set to 25 m/sec. so that a mixture was produced.
[0118] Styrene acrylic resin (weight-average molecular weight
20,000): 100 parts by weight Anatase-type titanium oxide (average
primary particle size 150 nm): 30 parts by weight
[0119] The above-mentioned mixture was kneaded by using a
twin-screw extrusion kneader, then coarsely pulverized by a hammer
mill, and subjected to a grinding process by using a Turbomill
grinder (made by Turbo Kogyo Co., Ltd.) and furthermore subjected
to a fine powder classifying process by using an air-flow
classifier that utilizes the Coanda effect so that white base
particles, having a volume-average particle size of 10.0 .mu.m,
were produced.
[0120] (Resin Fine Particles)
[0121] To 100 parts by weight of the above white base particles was
added 6.6 parts by weight of polyacrylic resin particles (average
primary particle size: 100 nm, Tg: 60.degree. C.), and this was
charged into a Henschel mixer (made by Mitsui Miike Mining Co.,
Ltd.), and mixed for 30 minutes, with a peripheral velocity of
stirring blades being set to 55 m/sec.
[0122] (Inorganic Fine Particles)
[0123] To this were successively added 0.9 parts by weight of
silica particles having an average primary particle size of 15 nm
that was treated by an amino silane coupling agent
(aminopropyltrimethoxy silane), and this was mixed for 5 minutes by
using a Hybridizer (made by Nara Machinery Co., Ltd.), with its
number of revolutions being set to 10,000 rpm, so that white
display particles were produced.
[0124] Thereafter, the resulting display particles were subjected
to an instantaneous heating treatment by using a hot-air spherizing
device (Surfusing System SFS-3; made by Nippon Pneumatic MFG.)
under conditions of an inlet hot-air temperature of 100.degree. C.,
a hot-air flow rate of 1.0 m.sup.3 and a material charging rate of
1.0 kg/h, with its hot-air treatment time being 0.03 sec.
[0125] Production of Black Display Particles
[0126] (Black Base Particles)
[0127] The following resin and carbon black were charged into a
Henschel mixer (made by Mitsui Miike Mining Co., Ltd.), and mixed
for 5 minutes, with a peripheral velocity of stirring blades being
set to 25 m/sec. so that a mixture was produced.
[0128] Styrene acrylic resin (weight-average molecular weight
20,000):
100 parts by weight
[0129] Carbon black (average primary particle size 25 nm): 10 parts
by weight
[0130] The above-mentioned mixture was kneaded by using a
twin-screw extrusion kneader, then coarsely pulverized by a hammer
mill, and then subjected to a coarse grinding process by using a
Turbomill grinder (made by Turbo Kogyo Co., Ltd.) and furthermore
subjected to a fine powder classifying process by using an air-flow
classifier that utilizes the Coanda effect so that black base
particles, having a volume-average particle size of 10.0 .mu.m,
were produced.
[0131] (Resin Fine Particles)
[0132] To 100 parts by weight of the above black base particles was
added 6.6 parts by weight of polyfluoroacrylic resin particles
(average primary particle size: 100 nm, Tg: 68.degree. C.), and
this was charged into a Henschel mixer (made by Mitsui Miike Mining
Co., Ltd.), and mixed for 30 minutes, with a peripheral velocity of
stirring blades being set to 55 m/sec.
[0133] (Inorganic Fine Particles)
[0134] To this were successively added 0.9 parts by weight of
silica particles having an average primary particle size of 15 nm
that was subjected to a dimethyldichloro silane treatment, and this
was mixed for 5 minutes by using a Hybridizer (made by Nara
Machinery Co., Ltd.), with its number of revolutions being set to
10,000 rpm, so that black display particles were produced.
[0135] Thereafter, the resulting display particles were subjected
to an instantaneous heating treatment by using a hot-air spherizing
device (Surfusing System SFS-3; made by Nippon Pneumatic MFG.)
under conditions of an inlet hot-air temperature of 100.degree. C.,
a hot-air flow rate of 1.0 m.sup.3 and a material charging rate of
1.0 kg/h, with its hot-air treatment time being 0.03 sec.
[0136] Carrier a Used for Charging White Display Particles
[0137] To 100 parts by weight of ferrite cores having an average
particle size of 80 .mu.m were added 2 parts of fluorinated
acrylate resin particles, and these materials were charged into a
horizontal rotation blade-type mixing machine, and mixed and
stirred for 10 minutes at 22.degree. C., with a peripheral speed of
the horizontal rotation blades being set to 8 m/sec., and this was
then heated at 90.degree. C., and stirred for 40 minutes so that
carrier A was produced.
[0138] Carrier B Used for Charging Black Display Particles
[0139] To 100 parts by weight of ferrite cores having an average
particle size of 80 .mu.m were added 2 parts of cyclohexyl
methacrylate resin particles, and these materials were charged into
a horizontal rotation blade-type mixing machine, and mixed and
stirred for 10 minutes at 22.degree. C., with a peripheral speed of
the horizontal rotation blades being set to 8 m/sec., and this was
then heated at 90.degree. C., and stirred for 40 minutes so that
carrier B was produced.
[0140] Production of Image Display Apparatus
[0141] An image display apparatus was manufactured by using the
following method so as to have the same structure as shown in FIG.
2(a). Two glass substrates 11, each having a length of 80 mm, a
width of 50 mm and a thickness of 0.7 mm, were prepared, and the
electrode 15 made of a coat film (resistance
30.OMEGA./.quadrature.) of indium-tin oxide (ITO) having a
thickness of 300 nm were formed on each of the substrates by a
vapor deposition method. On the above electrodes, a coating
solution, prepared by dissolving 12 g of polycarbonate resin in a
mixed solvent of 80 ml of tetrahydrofuran and 20 ml of cyclohexane,
was applied by using a spin coating method so that an insulating
layer 16 having a thickness of 3 .mu.m was formed; thus, a pair of
substrates with electrodes formed thereon were obtained.
[0142] Black display particles (1 g) and carrier B (9 g) were mixed
for 30 minutes by using a shaker (YS-LD, made by Yayoi Co., Ltd.)
so that the display particles were charged. The resulting mixture
(21, 210) was placed on a conductive stage 100 as shown in FIG.
6(a), and one of the substrates with electrodes formed thereto was
placed with a gap of about 2 mm interposed to the stage 100. A DC
bias of +50 V and an AC bias of 2.0 kV having a frequency of 2.0
kHz were applied between the electrode 15 and the stage 100 for 10
seconds so that the black display particles 21 were adhered onto
the insulating layer 16.
[0143] White display particles (1 g) and carrier A (9 g) were mixed
for 30 minutes by using a shaker (YS-LD, made by Yayoi Co., Ltd.)
so that the display particles were charged. The resulting mixture
(22, 220) was placed on a conductive stage 100 as shown in FIG.
6(b), and the other substrate with electrodes formed thereto was
placed with a gap of about 2 mm interposed to the stage 100. A DC
bias of -50 V and an AC bias of 2.0 kV having a frequency of 2.0
kHz were applied between the electrode 15 and the stage 100 for 10
seconds so that the white display particles 22 were adhered onto
the insulating layer 16.
[0144] The substrate with the electrode to which the black display
particles adhered and the substrate with electrode to which the
white display particles adhered were superposed as shown in FIG.
6(c) with a gap being adjusted to 50 .mu.m by partition walls, and
peripheral portions of the substrates were bonded to each other
with an epoxy adhesive so that an image display apparatus was
formed. The volume occupation rate of the two kinds of display
particles between the glass substrates was 50%. The occupation rate
between the white display particles and the black display particles
was set to virtually 1/1 in the number ratio of the white display
particles/the black display particles.
Examples 2 to 7, Comparative Examples 1 to 6
Production of White Display Particles and Black Display
Particles
[0145] White display particles and black display particles were
produced by using the same method as that of example 1, except that
white base particles and black base particles, produced by carrying
out a classifying process so that their volume-average particle
sizes became predetermined values, were used and that predetermined
amounts of predetermined resin fine particles and inorganic fine
particles were used.
Example 8
[0146] White display particles and black display particles were
produced by using the same method as that of example 1 except that
the instantaneous heating treatment was not carried out.
[0147] Production of Image Display Apparatus
[0148] An image display apparatus was manufactured by using the
same method as that of example 1 except that the white display
particles and black display particles obtained as described above
were used.
[0149] Evaluation
[0150] A DC voltage was applied to the image display apparatus
according to the following procedures, and the reflection density
of a displayed image obtained by the voltage application was
measured so that display characteristics were evaluated. The
voltage application was carried out through the following
procedures in which the voltage is applied in a manner so as to
follow a hysteresis curve having a route in which, after the
applied voltage is changed from 0V to the plus side, it is
successively changed to the minus side, and then again returned to
0V. That is:
[0151] (1) A voltage application is carried out while the voltage
is being varied from 0V to +100V with intervals of 20V.
[0152] (2) A voltage application is carried out while the voltage
is being varied from +100V to -100V with intervals of 20V.
[0153] (3) A voltage application is carried out while the voltage
is being varied from -100V to 0V with intervals of 20V.
[0154] In the case where the DC voltage was applied to each of the
image display apparatuses by using the above-mentioned procedures,
it was confirmed that, upon application of a plus voltage in a
white display state, the display was changed from white to black.
The voltage to be applied to the electrode on the upstream side in
the visually recognizing direction of the image display apparatus
was changed, with the electrodes on the other side being grounded.
The density was measured with a reflection densitometer "RD-918
(made by Macbeth Process Measurements Co.)".
[0155] The contrast was evaluated as one of display
characteristics, and the repeatability was furthermore
evaluated.
[0156] (Contrast)
[0157] The contrast was evaluated based upon a density difference
defined by a difference between the black density and the white
density, that is:
Contrast=Black Density-White Density
[0158] The black density corresponds to a reflection density of the
display surface obtained upon application of a voltage of +100V to
the electrode on the upstream side in the visually recognizable
direction of the image display apparatus.
[0159] The white density corresponds to a reflection density of the
display surface obtained upon application of a voltage of -100V to
the electrode on the upstream side in the visually recognizable
direction of the image display apparatus.
[0160] The density was measured with a reflection densitometer
"RD-918 (made by Macbeth Process Measurements Co.)" at each of five
positions randomly selected on the display surface, and the average
value was used.
[0161] The contrast was ranked under a three-grade criterion, that
is, superior (.largecircle.) when the density difference is 1.00 or
more, permissible (.DELTA.) when the density difference is 0.70 or
more, and impermissible (x) when the density difference is less
than 0.70.
[0162] (Repeatability)
[0163] The repeatability was measured by alternately repeating
voltage applications of +100V and -100V, and the reflection density
was measured each time, and when the contrast became 0.50, the
evaluation was made based upon the number of repetitions at this
time. When the number of repetitions was 5000 times or more, it was
evaluated as "superior (.largecircle.)", when the number of
repetitions was 1000 times or more, it was evaluated as
"permissible (.DELTA.), and when the number of repetitions was less
than 1000 times, it was evaluated as "impermissible (x)."
[0164] (Minimum Driving Voltage)
[0165] When an application voltage was varied from 0V to 200V with
intervals of 5V, the voltage, obtained at the time when the value
of the display density became 0.7 or more, was defined as the
maximum driving voltage. When the minimum voltage was 80V or less,
it was evaluated as "superior (.largecircle.)", when the minimum
voltage was 100V or less, it was evaluated as "permissible
(.DELTA.), and when the minimum voltage was more than 100V, it
state was evaluated as "impermissible (x)."
[0166] (Fixing Rate)
[0167] The fixing rate was measured on display particles composed
of white display particles and black display particles having the
same amount that were mixed with each other, by using the following
method. First, the BET specific surface area of the display
particles (BET specific surface area A) was measured by using a
Micromeritics JEMINI 2360 (made by Shimadzu Corporation). Display
particles (4 g) were dispersed in 40 g of a 0.2% aqueous solution
of polyoxyethylphenyl ether, and moistened, and to this was then
applied ultrasonic wave energy for 5 minutes by a ultrasonic wave
type Homogenizer US-1200T (made by Nippon Seiki Co., Ltd.;
specification frequency: kHz), with the value of an ampere meter
showing an indicator value, attached to the main device, being
adjusted to 60 .mu.A (50 w). The resulting mixed solution was
suction-filtrated, and only the solid component on a filter paper
was sufficiently dried so that the BET specific surface property of
this sample was measured (BET specific surface area B). The fixing
rate was obtained from the following equation:
Fixing Rate (%)=(BET specific surface area B)/(BET specific surface
area A).times.100
TABLE-US-00001 TABLE 1 Example 1 Example 2 Example 3 Example 4
White Base D1 (nm) 10000 1000 50000 40000 display particles
particles A1 Resin Kind: D2 (nm) Polyacrylic Polyacrylic
Polyacrylic Polyacrylic fine resin 100 resin 30 resin 250 resin 40
particles Amount 6.6 0.1 200 1.5 B1 of addition (parts) Inorganic
Kind: D3 (nm) Silica treated by Silica treated by Silica treated by
Silica treated by fine amino silane amino silane amino silane amino
silane particles coupling agent 15 coupling agent 5 coupling agent
30 coupling agent 5 C1 Amount 0.9 0.01 30 0.9 of addition (parts)
Degree of 78 82 77 82 hydrophobicity (%) D1/D2 100 33 200 1000 D2
/D3 6.7 6.0 8.3 8.0 Black Base D1 (nm) 10000 1000 50000 40000
display particles particles A2 Resin Kind: D2 Polyfluoroacrylate
Polyfluoroacrylate Polyfluoroacrylate Polyfluoroacrylate fine (nm)
100 30 250 40 particles Amount 6.6 6.6 200 1.5 B2 of addition
(parts) Inorganic Kind: D3 Silica treated by Silica treated by
Silica treated by Silica treated by fine (nm) dimethyldichloro
dimethyldichloro dimethyldichloro dimethyldichloro particles silane
15 silane 5 silane 30 silane 15 C2 Amount 0.9 0.01 30 0.9 of
addition (parts) Degree of 92 95 89 92 hydrophobicity (%) D1/D2 100
33 200 1000 D2/D3 6.7 6.0 8.3 2.7 Evaluation Contrast .largecircle.
(1.4) .DELTA. (0.95) .DELTA. (0.88) .DELTA. (0.72) Minimum driving
.largecircle. (75 V) .DELTA. (95 V) .DELTA. (85 V) .DELTA. (85 V)
voltage Repeatability .largecircle. .largecircle. .largecircle.
.DELTA. Fixing rate (%) 95 85 82 72 Example 5 Example 6 Example 7
Example 8 White Base D1 (nm) 40000 2500 10000 10000 display
particles particles A1 Resin Kind: D2 (nm) Polyacrylic Polyacrylic
Polyacrylic Polyacrylic fine resin 250 resin 250 resin 30 resin 100
particles Amount 150 200 2.5 6.6 B1 of addition (parts) Inorganic
Kind: D3 (nm) Silica treated by Silica treated by Silica treated by
Silica treated by fine amino silane amino silane amino silane amino
silane particles coupling agent 5 coupling agent 5 coupling agent
15 coupling agent 15 C1 Amount 0.05 0.05 0.1 0.9 of addition
(parts) Degree of 82 82 78 78 hydrophobicity (%) D1/D2 160 10 333
100 D2 /D3 50.0 50.0 2.0 6.7 Black Base D1 (nm) 40000 2500 10000
10000 display particles particles A2 Resin Kind: D2
Polyfluoroacrylate Polyfluoroacrylate Polyfluoroacrylate
Polyfluoroacrylate fine (nm) 250 250 30 100 particles Amount 150
150 2.5 6.6 B2 of addition (parts) Inorganic Kind: D3 Silica
treated by Silica treated by Silica treated by Silica treated by
fine (nm) dimethyldichloro dimethyldichloro dimethyldichloro
dimethyldichloro particles silane 5 silane 5 silane 15 silane 15 C2
Amount 0.05 0.05 0.1 0.9 of addition (parts) Degree of 95 95 92 92
hydrophobicity (%) D1/D2 160 10 333 100 D2/D3 50.0 50.0 2.0 6.7
Evaluation Contrast .DELTA. (0.98) .DELTA. (0.70) .DELTA. (0.81)
.DELTA. (0.95) Minimum driving .DELTA. (95 V) .DELTA. (100 V)
.DELTA. (90 V) .DELTA. (85 V) voltage Repeatability .largecircle.
.DELTA. .DELTA. .DELTA. Fixing rate (%) 88 70 75 52
TABLE-US-00002 TABLE 2 Comparative Comparative Comparative Example
1 Example 2 Example 3 White Base particles D1 900 55000 40000
display A1 (nm) particles Resin fine Kind: D2 Polyacrylic
Polyacrylic Polyacrylic particles (nm) resin 25 resin 270 resin 30
B1 Amount of 0.09 220 1.5 addition (parts) Inorganic Kind: D3
Silica treated by Silica treated by Silica treated by fine (nm)
amino silane amino silane amino silane particles coupling coupling
coupling C1 agent 4 agent 40 agent 5 Amount of 0.009 40 0.9
addition (parts) Degree of 80 75 82 hydrophobicity (%) D1/D2 36 204
1333 D2/D3 6.3 6.8 6.0 Black Base particles D1 900 55000 40000
display A2 (nm) particles Resin fine Kind: D2 Polyfluoroacryl
Polyfluoroacryl Polyfluoroacryl particles (nm) 25 970 30 B2 Amount
of 0.09 220 1.5 addition (parts) Inorganic Kind: D3 Silica treated
by Silica treated by Silica treated by fine (nm) dimethyldichloro
dimethyldichloro dimethyldichloro particles silane 4 silane 40
silane 15 C2 Amount of 0.009 40 0.9 addition (parts) Degree of 94
86 92 hydrophobicity (%) D1/D2 36 204 1333 D2/D3 6.3 6.8 2.0
Evaluation Contrast X(0.62) X(0.68) X(0.52) Minimum driving voltage
X(150 V) X(110 V) X(150 V) Repeatability X X .DELTA. Fixing rate
(%) 95 48 70 Comparative Comparative Comparative Example 4 Example
5 Example 6 White Base particles D1 40000 2000 10000 display A1
(nm) particles Resin fine Kind: D2 Polyacrylic Polyacrylic
Polyacrylic particles (nm) resin 270 resin 250 resin 30 B1 Amount
of 150 200 2.5 addition (parts) Inorganic Kind: D3 Silica treated
by Silica treated by Silica treated by fine (nm) amino silane amino
silane amino silane particles coupling coupling coupling C1 agent 5
agent 5 agent 20 Amount of 0.05 0.05 0.1 addition (parts) Degree of
82 82 78 hydrophobicity (%) D1/D2 148 8 333 D2/D3 54.0 50.0 1.5
Black Base particles D1 40000 2000 10000 display A2 (nm) particles
Resin fine Kind: D2 Polyfluoroacryl Polyfluoroacryl Polyfluoroacryl
particles (nm) 260 250 30 B2 Amount of 150 150 2.5 addition (parts)
Inorganic Kind: D3 Silica treated by Silica treated by Silica
treated by fine (nm) dimethyldichloro dimethyldichloro
dimethyldichloro particles silane 5 silane 5 silane 20 C2 Amount of
0.05 0.05 0.1 addition (parts) Degree of 95 95 92 hydrophobicity
(%) D1/D2 154 8 333 D2/D3 52.0 50.0 1.5 Evaluation Contrast X(0.52)
X(0.68) X(0.42) Minimum driving voltage X(160 V) X(120 V) X(120 V)
Repeatability .largecircle. .largecircle. .DELTA. Fixing rate (%)
85 90 78
REFERENCE SIGNS LIST
[0168] 1: Base particles, [0169] 2: Resin fine particles, [0170] 3:
Inorganic fine particles [0171] 10: Image display apparatus [0172]
11:12: Substrate [0173] 15: Electrode [0174] 16: Insulating layer
[0175] 17: Partition wall [0176] 18: Gap [0177] 18a: Image display
surface [0178] 21: Black display particles [0179] 22: White display
particles
* * * * *